As an example of a wind power generation device of the background art, a wind force is received by a blade to rotate a main shaft connected to the blade, and a speed-up gear is used for increasing the speed of the rotation of the main shaft to drive a power generator. As illustrated in FIG. 23, such a speed-up gear 202 includes a planetary gear mechanism 203 that receives the rotation of a main shaft 200 to increase its speed; a high-speed stage gear mechanism 204 that receives the rotation increased in speed by the planetary gear mechanism 203 to further increase its speed; and an output shaft 205 outputting the running torque of the high-speed stage gear mechanism 204.
In the planetary gear mechanism 203, when an input shaft 203a integrally rotatably connected to the main shaft 200 is rotated, a planetary carrier 203b is rotated to rotate a sun gear 203d at an increasing speed via a planetary gear 203c, so that the rotation of the sun gear can be transmitted to a low-speed shaft 204a of the high-speed stage gear mechanism 204.
In the high-speed stage gear mechanism 204, when the low-speed shaft 204a is rotated, an intermediate shaft 204d is rotated at an increasing speed via a low-speed gear 204b and a first intermediate gear 204c, so that the output shaft 205 can be rotated at an increasing speed further via a second intermediate gear 204e and a high-speed gear 204f. 
As bearings for rotatably supporting the low-speed shaft 204a, the intermediate shaft 204d and the output shaft 205 of the speed-up gear 202, roller bearings 206 to 211 are frequently used (see, for example, Patent Document 1).